Conventionally, as shift switching mechanisms switching a shift position of an automatic transmission by an actuator according to manipulation of a shift lever by a driver, those equipped with an electric motor (for example, a direct current motor) as a motive power source for switching a shift position have been known.
According to a shift switching mechanism as described above, there is no need to mechanically connect a shift lever and the shift switching mechanism as in a common switching mechanism that directly switches a shift position of an automatic transmission using manipulation force applied to a shift lever by a driver. Therefore, there is no limitation in layout when these components are mounted in a vehicle, and thus the degree of freedom in design can be increased. Further, there has been an advantage that mounting to a vehicle can be easily performed.
As a shift lever in such a shift switching mechanism, a momentary-type shift lever may be used. In the momentary-type shift lever, switching to a drive position such as the R, N, D, or B position and switching from the P position is performed according to manipulation of the shift lever starting from a reference position. The shift lever is provided with a shift sensor sensing movement of manipulation in a longitudinal direction and a select sensor sensing movement of manipulation in a lateral direction. Based on outputs from these sensors, a shift position is determined.
As a shift lever as described above, for example, Japanese Patent Laying-Open No. 2005-7993 discloses a shift device of a transmission appropriately responding to a driver's request in the shift device with a momentary function. The shift device of a transmission is a shift device of a transmission including a path for reaching a plurality of shift positions, and a momentary-type movable portion manipulated so as to move along the path by a driver. The movable portion is held at a predetermined reference position when it is not manipulated by the driver. The shift device includes recognition means for recognizing a shift position requested by the driver from holding of the movable portion at the shift position for a predetermined recognition time, and output means for outputting a control signal to the transmission so as to attain a power transmission state corresponding to the recognized shift position. The path includes the reference position, a first shift position representing one of the plurality of shift positions, and a second shift position representing one of the plurality of shift positions and provided between the reference position and the first shift position. When it is recognized that the movable portion is located at the first shift position, the power transmission state by the transmission is set to a first state. When it is recognized that the movable portion is located at the second shift position, the power transmission state by the transmission is set to a second state different from the first state. The shift device further includes setting means for setting the recognition time in accordance with a moving direction of the movable portion along the path.
According to the shift device of a transmission, a time for recognizing the second shift position in a first case where the driver performs manipulation based on a request to bring the power transmission state by the transmission into the second state and the movable portion is located at the second shift position, and a time for recognizing the second shift position in a second case where the movable portion comes to the second shift position on its way to return to the reference position can be set separately. Therefore, the driver's request can appropriately be recognized based on a time for which the movable portion is held at the second shift position.
However, if an abnormality occurs in a sensor during detection of the position of a shift lever with a select sensor and a shift sensor, a parking lock cannot be released depending on the state of the abnormality. For example, in a case where an abnormality occurs in the select sensor while it is detecting the position of the shift lever in a direction in which the shift lever is moved between the reference position and a neutral position, if it is unclear whether switching to the neutral position is performed, there is a possibility that a parking position cannot be released.
This is because, when the select sensor is abnormal, if position detection by the select sensor is not performed after switching to the parking position is performed, or if it is unclear whether switching to the neutral position is performed, it is also unclear whether switching to a forward drive position or a reverse drive position is performed. Therefore, it is impossible to release the parking position according to the intention of the driver when the select sensor is abnormal.
If it is impossible to release the parking position according to the intention of the driver, the parking lock cannot be released. Accordingly, for example, it is impossible to move a disabled vehicle by pushing the same with hands or using a tow truck or the like. In the aforementioned publication, the problems described above are not considered at all, and thus cannot be solved.